The main quests of the questline start with "Shattered Seas: ", during those signature quests you'll often have to complete some solo quests.
There are also some other solo quests avalible that don't count for the "Shattered Seas: " signature, but they give gear/jewelry and may unlock items at the armor trading merchant in Phantom Sea.

Putting Down the Walking Dead(benefit: Malignant Shadows will no longer knock you out of the sky in the larger region BUT the Cursespinners will still knock you out of the sky if you get too close to Ghorkaal. )